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LIBRARY OF CONGRESS 




014 638 884 A # 



UNITED STATES DEPARTMENT OF AGRICULTURE 




JPU3P"<KJTL. 



% BULLETIN No. 1055 A 



Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 




S\J9*^Lru 



Washington, D. C. 



May 10, 1922 



METHODS OF MANUFACTURING POTATO CHIPS. 



TX 803 
.P8 V6 
Copy 1 



jaret Connor Vosbury, Scientific Assistant, Office of Horticultural and 
" Pomological Investigations. 



CONTENTS. 



Tage. 



Introduction 

Experimental methods of making po- 
tato chips 

Fats used in the experimental work- 
Standard method of making chips for 

the tests 

Handling the fat in making chips 

Equipment 



Page. 

Selecting potatoes for chips 11 

Causes of failure in making chips 12 

Score card used in these tests 1-3 

Comparative adaptability of varieties 

for making chips 14 

Loss in peeling and quantity of chips 

obtained 16 

Summary 19 



INTRODUCTION. 

Potatoes are a universal food and share honors with bread as the 
" staff of life." There is only one style, however, in which cooked 
potatoes are now distributed in commercial quantities over long dis- 
tances in a condition to keep for a considerable time. Crisp, golden 
potato chips command a ready market in all seasons, and there are 
firms which supply markets a thousand miles away. Moreover, it is 
not difficult to prepare them at home with ordinary household equip- 
ment if a few fundamental rules are observed. 

Beginning in 1914, there has been conducted each winter a series 
of cooking experiments designed to test the culinary value of a large 
number of the most promising of the seedling tubers developed in 
the potato-breeding project of the Office of Horticultural and Pomo- 
logical Investigations of the Bureau of Plant Industry, United 
States Department of Agriculture. During the first three years a 
special study was made of methods of making potato chips and the 
value of the different seedlings for that purpose. 

The first year's work, 1914—15, was largely experimental, methods 
of procedure being developed and standardized. The tests were 
continued and amplified during 1915-16 and 1916-17. No effort was 

82277°— 22 1 



Monograph 



2 BULLETIN 1055, U. S. DEPARTMENT OF AGRICULTURE. 

made to study commercial varieties systematically, but a number of 
the varieties from the departmental collection were tested during 
the course of the three years. These included several varieties from 
each of Stuart's 1 eleven groups or families. All of these potatoes 
were grown by the Office of Horticultural and Pomological Investi- 
gations on the State Experimental Farm at Presque Isle, Aroostook 
County, Me. Cultural and weather conditions varied somewhat dur- 
ing the seasons, but the comparison between different varieties is 
substantially correct, especially between tubers grown in any one 
year. The potatoes were shipped to Washington each fall and kept 
in cold storage at the Arlington Experimental Farm until needed. 
The general results obtained in the cooking tests have been sum- 
marized and are presented here. 

EXPERIMENTAL METHODS OF MAKING POTATO CHIPS. 

In starting these tests it was first of all important to determine 
the best methods of making chips, the most satisfactory frying me- 
dium, and the most efficient equipment to use. The Green Moun- 
tain variety of potato was taken as the standard of comparison. The 
methods employed naturally had to be those adapted to home rather 
than to commercial usage, because of laboratory limitations in equip- 
ment and supplies; but it was intended to make the tests comply 
with commercial practices in so far as it was possible. 

The following recipe for potato chips by Farmer 2 was used as a 
basis for the investigation : 

Wash and pare potatoes. Slice thinly (using a vegetable slicer) into a bowl 
of cold water. Let stand two hours, changing water twice. Drain, plunge 
in a kettle of boiling water, and boil one minute. Drain again and cover with 
cold water. Take from water and dry between towels. Fry in deep fat until 
light brown, keeping in motion with a skimmer. Drain on brown paper and 
sprinkle with salt. 

The partial cooking in boiling water was supposed to keep the 
potato from absorbing much of the fat in which it was fried, result- 
ing in a less greasy product and was, of course, a slightly more eco- 
nomical one, as less grease was consumed. The recipe was followed, 
with variations, during the preliminary work in 1914-15. Though 
good chips were secured, the method was not found to be entirely 
satisfactory, as it entailed too much labor. A study of the methods 
in use in commercial plants demonstrated that the hot-water bath 
was neither practicable nor necessary. The problem was to produce 

'Stuart, William. Group classification and varietal descriptions of some American 
potatoes. U. s. Dept. Agr. Bui. 176, 56 p., 19 pi. 1915. 

- Farmer. Fannie Merritt. The Boston Cooking-School Cook Book . . . p. 314. Boston, 
1017. 



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ST) .y r METHODS OF MANUFACTURING POTATO CHIPS. 3 

first-class chips by methods as simple as possible, equally applica- 
ble at home or in a factory. The following methods were tried : 

(1) Following the recipe given above. 

(2) Washing in cold water, which was then shaken off; not dried. 

(3) Washing in cold water; dipping in hot water; not dried. 

(4) Washing in cold water; dried between towels. 

(5) Washing in cold water, dipping in hot and again in cold water; not 
dried. 

(6) Washing in cold salt water and then in clear, cold running water; 
dipping in hot water ; then in cold water and dried. 

(7) Soaking in cold water for 24 hours; dipping in hot water; again in cold 
water ; dried. 

(8) Not washed or dried; fried as soon as sliced. 

(9) Not washed; dried before frying. 

(10) Dipping in hot water immediately after slicing; then in cold; drained 
but not dried. 

Some of these methods produced good chips. Certain others, 
notably Nos. 8, 9, and 10, resulted in a distinctly poor product, soggy 
and uneven. There was no apparent advantage from the use of the 
salt-water bath in No. 6. Nor was it found that the hot-water bath 
was at all essential to producing crisp, nongreasy, high-grade chips. 
Cutting the potatoes into thin, even slices with an accurate vegetable 
slicer, soaking them thoroughly in clear, cold water after an initial 
bath of cold running water, and frying them in a clean, high-grade 
fat at a high temperature were found to be the three essentials in 
producing crisp, high-quality chips. 

FATS USED IN THE EXPERIMENTAL WORK. 

Deep- fat frying to the minds of many housekeepers means frying 
in lard, and many cookbook recipes for potato chips specify the use 
of lard. Pure leaf lard, therefore, headed the list of fats which were 
experimented with. Then came various lardlike derivatives of cot- 
tonseed oil, half a dozen standard brands of cottonseed oil, several 
samples of peanut oil, coconut oil, and a mixture of lard and beef 
suet. 

The most satisfactory frying medium was found to be a high- 
grade cottonseed oil, and this was adopted as the standard in sub- 
sequent cooking tests. Good cottonseed oil was clear and bland and 
practically flavorless. It proved to be the most economical fat, both 
because of a lower initial cost and a minimum of waste in cooking; 
and a comparison of chips fried in the different fats demonstrated 
its superiority in behavior during cooking and in the flavor of the 
finished product. Both the lard and the lard and suet mixture im- 
parted a flavor or aftertaste that was unpleasant to some people and 
left a cloud} 7 coating on the. chips that made them less attractive 
than the clear yellow-brown gloss of chips fried in oil. All the vege- 



BULLETIN 1055, U. -S. DEPARTMENT OF AGRICULTURE. 



table oils and compounds were more satisfactory than the animal 
fats. The liquids were preferred to the semiplastic compounds, be- 
ing more convenient to use in quantities, less expensive, and less 
wasteful in utilization. 

Most manufacturers of commercial potato chips use cottonseed oil, 
a few use lard, and a few have experimented with coconut and corn 
oils. Peanut oil is not yet widely known and has been so far little 
used in the manufacture of potato chips, but there is no reason why 
satisfactory results should not be obtained if a highly refined, bland 
oil is put on the market at prices that will compete with the cotton- 
seed oil now in use. 

The smoking point of well-refined cottonseed oil is higher than that 
of most of the other frying mediums, a much more important factor 




Fig. 1. — First step in making potato chips. Weighing six medium-sized potatoes on a 

torsion balance. 

in frying potato chips than in frying doughnuts, fritters, or similar 
foods that must be cooked through as well as browned. Blunt and 
Feeney 3 have determined the burning point of a number of the cook- 
ing fats, and their investigations show that cottonseed oil has the 
highest burning point, 451° F. (232.7° C), with two cottonseed oil 
derivatives very nearly the same, 450° F. (232.2° C), and 448° F. 
(231.1° C). Leaf lard smoked at 430° F. (221.1° C), bulk lard at 
381° F. (194.0° C.) ; olive oil at 347° F. (172,7° C.) ; two samples of 
peanut oil at 323° F. (161.6° C.) and 300° F. (148.8° C), respec- 
tively; and coconut oil at 277° F. (136.1° C). 

Some of the samples of peanut oil used in these investigations wore 
almost as highly refined as the cottonseed oil and had as high a smok- 
ing point, but others smoked at approximately as low a temperature 



"Blunt, Catharine, and Feeney, Clara M. The smoking temperature of edible fats. 
Jour. Home Keon., v. 7, No. 10, pp. 535-541. 1915. 



In 



METHODS OF MANUFACTURING POTATO CHIPS. 5 

as the two samples used by Blunt and Feeney. The coconut oil used 
in the chip experiments of the United States Department of Agricul- 
ture smoked at a temperature of 338° F. (170° C), higher than the 




Fig. 2. — Removing eyes and diseased spots from peeled potatoes. 

figures given by Blunt and Feeney, but still too low for satisfactory 
results. Olive oil was not tried ; its expense prohibits its use as a com- 
mercial frying medium. According to Blunt and Feeney, however, 



6 BULLETIN 1055, U. S. DEPARTMENT OF AGRICULTURE. 

its smoking point is too low to make it a competitor of the cheaper 
oils. No fat with a smoking point of less than 220° C. (428° F.) is 
desirable for frying potato chips. Overheated fat is unwholesome 
and imparts a scorched flavor to the food. 

STANDARD METHOD OF MAKING CHIPS FOR THE TESTS. 

As a result of the first year's experiments, the following uniform 
method of procedure was developed and used as a standard : 

Six or seven medium-sized potatoes, with a total weight of approxi- 
mately 1,000 grams, were first weighed on a torsion balance (fig. 1), 
then peeled in a vegetable peeler, all eyes or diseased spots removed 
(figs. 2 and 3), and the peeled potatoes weighed again. They were 
then sliced with a vegetable cutter into slices one-sixteenth of an inch 
thick; these slices were weighed (fig. 4) and put to soak in cold water, 
care being taken to keep each lot or variety in a separate pan. Each 
lot was washed in cold running water until the next lot had been 
weighed, peeled, sliced, and weighed again. It was then placed in a 
pan of cold water, while the second lot took its place under the faucet 
of running water (fig. 5) . By the time the last lot had been prepared 
and placed under the faucet, the first lots had been soaking in cold 

water for several 

' .$g$$&*rg, '; ' ;■ !,.. vO-'f u,v, Cl? MPl£> hours. The water m 

the pans was changed 
until the last wash 

Fig. 3. — Small apple corer or vegetable peeling knife used wa terS Were practi- 

to remove eyes and diseased spots from potatoes. Thero ■" ■-"' 

is a blade at tbe side, and if a mechanical peeler is not Cally free of starcri. 

available knives of this, description are better for peeling The frvino* Pail 

tban ordinary paring knives. ^ te « i 

and oil were weighed 
before and after the chips were cooked, to determine just how much 
oil was used in making a given weight of chips. A thermometer 
was hung in the frying pan, the bulb being covered with oil, in 
order that uniform temperatures might be secured for each experi- 
ment. When the oil reached 210° C. (410° F.) the thermometer 
was removed to another pan of hot oil, the inner basket containing 
the raw sliced potatoes lowered into the hot fat (fig. 6), and the 
slices stirred constantly with a long-handled spoon. The slices 
were not dried, but as much of the water as possible was removed 
by shaking before lowering them into the hot fat. When the water 
on the potatoes had boiled away and the slices were crisp and 
golden brown, the frying basket was raised, the excess oil drained 
off, and the chips emptied on brown paper to dry (fig. 7). They 
were later weighed (fig. 8), sprinkled lightly with salt, and scored by 
the three judges. 




.METHODS OF MANUFACTURING POTATO CHIPS. 7 

HANDLING THE FAT IN MAKING CHIPS. 

If the sliced potatoes are put into oil which is at a low temperature, 
they take a long time to fry and absorb so much grease that they are 
both soggy and unpalatable. Moreover, the more grease consumed in 
frying, the greater the expense of the product. The aim of the hot- 
water bath in Miss Farmer's 4 recipe was to coagulate the protein in 
the potatoes, thus searing the surface and making it impossible for 
much grease to soak in. The same result may be attained by heating 
the oil to a point just below smoking before the slices are put in. 
The higher the temperature that can be maintained, the sooner the 
surface of the potato will be crusted over and the less oil will pene- 
trate. The water on the raw sliced potatoes and the temperature of 
the inner frying basket itself will lower the initial temperature of the 




Fig. 4. — Weighing the slices of potatoes to determine the total loss in peeling and slicing. 

oil, and it will take several minutes for the water to boil away and the 
fat to regain the heat it lost. Fats do not " boil." It is the water in 
the oil that makes it bubble when heated, and until this has been 
changed to steam and evaporated the temperature of the fat can not 
be raised much above 100° C. (212° F.). The hotter the initial tem- 
perature of the oil, the more quickly the water will be boiled away. 
As the water evaporates, the oil becomes still and the temperature in- 
creases rapidly. It should be reheated after each batch of chips is re- 
moved. The only certain laboratory method of determining the tem- 
perature of the fat is to suspend a thermometer in the center of the 
pan. 



1 Farmer, Fannie Merritt. Op. cit. 



8 BULLETIN 1055, U. S. DEPARTMENT OF AGRICULTURE. 

Oil can not be used indefinitely without being renewed. After 
prolonged use of the oil the chips do not brown well and take too 
long to cook. Much foreign matter has been absorbed by the oil, 
which can not be removed by the most careful straining. It should 
be thrown away or used for soap grease. The common practice in 
potato-chip factories is to replace what is used up in the cooking 
process by adding fresh oil. This, however, should not be continued 
indefinitely, entirely fresh oil being required at least every few days. 
The most successful potato-chip factory which was visited makes a 
practice of renewing the oil every second or third day. The small 
particles of potato are skimmed out after every batch of chips is re- 
moved and all the oil carefully filtered each night after the close of 
business. New oil is added as needed during the day, and every sec- 




Fig. 5. — Soaking the different lots of potatoes in pans of cold water preparatory to frying 
into chips. The last lot is still under the faucet of running water. 

ond or third night the contents of the kettles are emptied and sold 
for soap grease. The result is a high-quality potato chip that will 
keep sweet for weeks. Some manufacturers make no effort to renew 
their oil entirely, simply adding fresh oil as needed. As a result the 
oil is never entirely sweet ; and the old, worn-out oil which is always 
present affects the ease of cooking, the flavor, and the keeping quality 
of the chips. 

In the refined cottonseed oil sold for cooking purposes there is re- 
markably little of the foreign matter from which the oil is expressed. 
Small particles of such foreign matter act as ferments if left in the 
oil and set free fatty acids which make the oil turn rancid and lower 
its smoking point. Chips can be cooked at a higher temperature in 
oil that is free from such impurities than in oil that has not been 
as highly refined. The small particles of fried potato or of the plant 
from which the oil is expressed burn and smoke at a comparatively 
low temperature and impart a scorched flavor to the oil, which is 



METHODS OF MANUFACTURING POTATO CHIPS. 



9 



transmitted to the chips. Hence the importance of buying high-grade 
oil and of carefully skimming out little particles of potatoes after 
each batch of chips is removed. 

EQUIPMENT. 

The mechanical peelers have been found very satisfactory as time, 
labor, and food savers. Of course, in the average household vege- 
tables are not prepared in quantities large enough to make necessary 
the purchase of such equipment, but in restaurants, hotels, or large 
establishments they are found very serviceable. In potato-chip fac- 




Fig. (J. — Lowering the inner basket full of raw sliced potatoes into the hot oil. 
thermometer is now hung in the kettle at the left. 



Tlv 



tories they are indispensable, and every chip factory has one or more 
large power machines. Figure 9 shows the small hand-power peeler 
which was used in the potato-chip experiments. Six or eight po- 
tatoes were peeled simultaneously. The loss in paring was less 
than by ordinary hand peeling, for the sharp edges of the carborun- 
dum lining nicked off the skin without cutting deeply into the flesh. 
The loss was least, of course, when the potatoes were smooth and 
regular, as the abrasion tended to wear down knobs and irregularities 
and leave the potatoes round or oval-oblong in shape. Deep eyes or 
bad spots had to be removed by hand, however. One of the small 
82277°— 22 2 



10 



BULLETIX 1055, U. S. DEPARTMENT OF AGRICULTURE. 



apple corers and vegetable peeling knives retailing at 10 or 15 cents 
(figs. 2 and 3) was used for this purpose. In potato-chip factories 
a number of women or girls are employed to go over the potatoes as 
they are emptied from the peeler to cut out the eyes and imperfect 
places. 

Some form of vegetable slicer is essential, as it is impossible to 
slice the potatoes thinly enough and evenly enough by hand. Satis- 
factory slicers may be obtained, either turned by hand power or 
motor driven. A small hand-power slicer used in 1914-15 did not 
prove satisfactory for laboratory tests, for the slices were thicker at 




Fig. 7. — Draining the excess oil from the potato chips by spreading them on brown paper. 

one side than the other, because of an imperfection in the casting of 
the knives. As it was necessary to secure uniformly even slices for 
experimental work, a larger slicer, also hand driven, was obtained 
at the beginning of the 1915-16 season (fig. 10). A number of large 
power-driven mechanical slicers, suitable for use in factories, are 
on the market. 

When making chips at home the slices may be soaked in any kind 
of pans that are available. In factories they are generally soaked 
in tubs with fresh water fed in through rubber hose or in big 
tanks especially built for the purpose with fresh water flowing in 
at one end and an outlet pipe at the other end to carry off the wash 
water and starch. When working with large quantities it is gener- 
ally found worth while to salvage the potato starch deposited by 
this wash water and by the waste from the potato peeler. 



METHODS OF MANUFACTURING POTATO CHIPS. 



11 



The best vessel in which to fry the chips is one that is deep rather 
than wide, with an inner perforated basket in which the chips can be 
lowered and raised. Steel friers in two parts, which are suitable for 
frying chips, croquettes, chicken, etc., can be obtained at hardware 
stores. Practically every family has some kettle suitable for deep-fat 
frying, and if necessary the inner basket can be improvised from steel 
wire. These frying pans should be of iron or steel, which is not 
affected by the highest cooking temperature. It is not safe to use tin 
or enamel-ware pans, which melt or chip off when very hot. Most 
potato-chip factories have large frying kettles built to suit their par- 
ticular requirements, sometimes round, sometimes oblong in shape, 
and with special heating equipment for either gas or coal. Gener- 
ally the kettles are built in one piece with the stoves. In some cases 




Fig. 8.- — Weighing the chips, the last step before they are salted and judged. 

inclined boards at one end on which the chips are emptied as skimmed 
out of the oil serve as drains to carry the surplus oil back into the 
tank or kettle. The sliced potatoes are lowered into the oil in heavy 
wire baskets made to fit the shape of the kettles. Sometimes, in- 
stead of frying baskets being used, the raw slices are emptied directly 
into the oil and the chips removed with perforated scoops or long- 
handled wire skimmers. 



SELECTING POTATOES FOR CHIPS. 

Not every potato will make a good chip, and the excellence of the 
finished product, here as elsewhere, depends on the materials used 
and the care exercised in their preparation. The following require- 
ments should be observed when selecting potatoes for chips : 

Use mature potatoes. New potatoes in the spring or early summer do not 
make good chips. They should not be used before the skin sets. Manu- 



12 



BULLETIN 1055, U. S. DEPARTMENT OF AGRICULTURE. 



facturers who use potatoes in large quantities are agreed that the old stock is 

preferable for chips to the immature potatoes of the spring or early summer. 
Use potatoes high in starch. A waxy or soggy potato does not make good 

chips. Select a variety that is known to be mealy when baked or boiled. 

The raw flesh should be firm and crisp when sliced with a sharp knife. 
Use large or medium-sized round, smooth potatoes with shallow eyes. The 

size and shape do not affect the cooking quality, but they do influence the 

quantity and appearance 
of the chips. Round po- 
tatoes are better than 
long ones, as there is 
less waste in peeling, 
especially if a vegetable 
peeler is used. Deep 
eyes are objectionable, 
because of the difficulty 
of paring and the waste 
involved and beca use 
they make ragged-look- 
ing slices. 

Care should be 
taken not to cook too 
many chips at once. 
The fat should be 
deep enough to cover 
the slices completely, 
and allow them to lie 
flat and be crusted 
over quickly. If the 
kettle is too full, the 
water on the raw 
slices will bubble 
high and splash over 
the sides of the pan 
or A^at. They cook 
quickly, the time re- 
quired varying witli 
the size of the kettle 
and the quantity of 
oil and potatoes used. 
Three to five minutes 
is a good average. If 




Fig. 9. — Small hand-power vegetable peeler. The potatoes 
are thrown by centrifugal motion against the carborun- 
dum lining, which nicks off the skin in small bits. Fresh 
water drips through the perforated pan at the top, carry- 
ing away the skins through the rubber waste pipe at the 
base. 



thev take longer something is wrong 



to ? 



either the oil is not hot enough 
or the quantity of potatoes cooked is too great in proportion. 

CAUSES OF FAILURE IN MAKING CHIPS. 

The troubles of commercial manufacturers are generally due to one 
or more of the three following causes: (1) The use of a potato 



METHODS OF MANUFACTURING POTATO CHIPS. 



13 



variety not adapted for making into chips. (2) Improper washing 
of the sliced potatoes. Some factories do not recognize the impor- 
tance of removing a maximum amount of starch. The result is a 
tough instead of a crisp chip. (3) Using the oil at too low a tem- 
perature and not renewing it frequently enough. When the oil is 
not hot enough the chips absorb too much grease, and when it is 
too old they have a burned or spoiled flavor and turn rancid quickly. 
Chips fried in fresh sweet oil should keep sweet for weeks unless 




Fig. 10. — Hand-power vegetable elicer purchased at the beginning of the 1916 season. 

subjected to very high temperatures and should permit long-distance 
shipment. 

SCORE CARD USED IN THESE TESTS. 

The form of the score card used in keeping a record of each lot of 
potato chips is shown here. The markings were all numerical, with 
the exception of the two subdivisions, " shape " and " desirability," 
under " tubers." Shape might be designated either by a descriptive 
term, such as flat, round, oval, etc., or by a pencil sketch. Symbolic 
markings, with the following divisions — very good, good, medium, 
poor, and very poor — indicated the desirability of each lot, as shown 



14 



BULLETIN 1055, U. S. DEPARTMENT OF AGRICULTURE. 



by their general appearance and shape. The different weights of the 
tubers were recorded in grams. While the standard temperature of 
the fat was 210° C. and endeavor was made to raise the temperature 
of the oil to that point for each test, there were variations, especially 
when different frying media were being experimented with. Provi- 
sion was made in one column, therefore, for keeping a record of the 
temperature at which each lot was cooked. 

SCORE CAED USED IN POTATO-CHIP TESTS. 



Variety Accession No 

Grown at Picked Shipped 

Stored in at * Out . 

Test Potato chips. Frying medium Date 



Tubers. 


Weight. 


Tem- 
pera- 
ture 
of fat 
(° F.). 


Cook- 
ing 
time 
(min- 
utes). 


Ease 

of 
cook- 
ing 
(10). 


Ap- 
pear- 
ance 

(5). 


Crisp- 
ness 

(5). 


Fla- 
vor 
(10). 


Total 
score 
(30). 


Num- 
ber. 


Shape. 


Desir- 
abil- 
ity. 


Un- 
peeled. 


Peeled. 


Sliced 
raw. 


Chips. 























































































Method. 



Remarks. 



Ease of cooking was given 10 points out of a possible total score of 
30, the rating being necessarily left to the judgment of the person 
who conducted the tests. It was based on the general behavior of the 
potatoes in the hot fat, the length of time a lot of given quantity took 
to fry, and the uniformity with which the slices colored and became 
crisp. The other three subdivisons of the score were marked by the 
three judges who tested all the potatoes. Under "Appearance " (5 
points) the ideal was a clear, yellowish brown, flat chip. " Crisp- 
ness " (5 points) was marked high when the chips were dry and 
crisp, greasiness or unevenness in cooking lowering the score. Flavor 
(5 points) was, of course, largely a matter of individual preference. 
With fresh bland oil there is no heavy, greasy flavor to obscure the 
variations in the different potatoes. 

COMPARATIVE ADAPTABILITY OF VARIETIES FOR MAKING 

CHIPS. 

The total scores given the different seedlings from which potato 
chips were made during 1915, L916, and 1917, were averaged when 
several tests were made. 8 22723 ranked highest, with an average 



METHODS OF MANUFACTURING POTATO CHIPS. 



15 



score of 28.4 for two seasons' tests, 27.2 in 191G and 20.7 in 1917. In 
a 1-season test there was only one seedling whose total score exceeded 
29.7, and that was S 38595 with 29.8, a difference so slight as to be 
negligible. Many of the seedlings graded 29.0 or more, however. 
The lowest average score was 20.9, given to S 7322, and the lowest 
single score was 12.3, given to S 1449. In this connection, it should 
be borne in mind that those potatoes which were evidently unsuited 
for chips were not subjected to this test. 

Table 1. — Comparison of the adaptability for chips of standard varieties of 
potatoes tested in 1915, 1916, and 1911. 

[Based on a score of 30 for perfect.] 





Score for making chips. 


Group and variety. 


Score for making chips . 


Group and variety. 


1915 


1916 


1917 


Aver- 
age. 


I 
1915 1916 


1917 


Aver- 
age. 


Irish Cobbler: 

Irish Cobbler 


24.1 


23.5 


27.2 
28.8 
28.2 
29.5 
29.2 
27.9 

25.6 
26.5 
26.0 

28.0 
27.1 
28.6 
28.4 
25.5 
28.3 


24.9 
22.4 


Rural: 

Rural New Yorker . . 
Nonblight 


23.1 


27.3 


'26.' 3' 
28.6 
26.3 

24.3 
27.2 

23.2 
26.7 

'23.' 8* 

26.1 


25.2 


Early Beauty 


Pan American 








Early Victor 






Sensation. . . 








Flourball 






Sir Walter Raleigh... 
Todd's Wonder 








First Early 








New Early Standard. 






Russet Rural 








Triumph: 

Triumph 


19.2 




Pearl: 

Pearl... 


22.2 




22.7 


White Triumph 


Dearborn 




Wood's Earliest 






Peoples 




25.5 




Early Michigan: 

Early Michigan 






Blue Victor 






Peachblow: 

White Peachblow. . . 




25.3 




Early Albino 






25.7 


Early Harvest 






McCormick 


20.3 




Extra Early Sunlight 






White McCormick. . . 


24.9 






Dewdrop 






Up-to-Date: 

Factor 


27.5 
25.8 






Ehnola 








Early Rose: 


24.1 




Up-to-Date 


25.1 


26.3 
26.8 
26.1 
23.1 

29.5 


25.7 


Early R ose 


Bull Moose 




Early Walters 




24.2 
27.9 

27.3 

26.7 




Gold Standard 








Northern King 


28.2 


27.6 


Moreton 








Woodbury's White 
Rose 


Miscellaneous: 

British Queen 








Early Manistee 

Spaulding No. 4 


26.4 
18.7 
18.8 


.27.0 


Casseker Salathorn- 
chen 




23.0 




(Rose No. 4) 


Clio 




24.8 
28.7 
25.5 
26.7 
26.1 
26.8 
28.7 




Early Ohio: 


25.4 


27.1 

26.7 
27.5 

27.5 

26.6 

27.5 
25.5 

29.0 
26.5 
28.3 
28.6 
26.7 
27.4 
27.3 
29.5 
25.5 


23.7 
26.6 


Country Gentleman. 
Dalmeny Challenge. . 
Eldorado 








Early Ohio 


24.0 


27.0 
25.6 

25.1 




Acme 


26.1 


Early Dix 






Garnet Chili 


25.5 


25.8 


Hebron: 






Hamburger Eier 


25.9 


New White Hebron. 


Harvest King 






Burbank X Early 
Ohio 






Jones Pink Eyed 
Seedling 




19.1 




Burbank: 






Keeper 




26.0 
23.6 
25.2 
27.2 




Viking No. 1 


Mclntyre 




25.6 


24.6 


Netted Gem 


27.8 
24.2 


23.2 
26.6 


Maggie Murphy 






Green Mountain: 


New Era 








Green Mountain 


Pehuencha 




23.7 
20.0 




Green Mountain, Jr. . 


Prof. Maerker 




21.3 
25.4 
24.7 
24.7 
25.1 
17.8 
24.2 
24.9 


20.6 


Carman No. 1 






Perkin 's Seedling 






Gold Coin 






Rural Blush 




20.3 


22.5 


McKinley. . . 






Saxony 






Uncle Sam 






Sport of Garnet Chili . 








Wee McGregor 






Switez 




7.0 
10.1 


12.4 


American Wonder. . . 






Wohltmann 




17.1 


Longfellow 






Vitality 



















Table 1 summarizes the scores of those standard varieties of po- 
tatoes which were made into chips. The Green Mountain received the 



16 BULLETIN 1055. IT. S. DEPARTMENT OF AGRICULTURE. 

highest average score. 26.6, based on three years' tests. In the single 
season's scores there were three varieties that were tied for highest 
place, Flourball, American Wonder, and British Queen, all scoring 
29.5 in 1917. The lowest average score, 12.4, was given to Switez, one 
of the German starch varieties. This variety was not adapted for 
chip making and was merely tried to see how it would behave. The 
same may be said of the potato receiving the second lowest score, 17.1, 
Wohltmann, another German variety. The lowest 1-year score was 
given to Switez in 1916 also. 

LOSS IN PEELING AND QUANTITY OF CHIPS OBTAINED. 

Table 2 gives a 3-year average of the loss in peeling and the quan- 
tity of chips made from all lots, with detailed figures for a few of 
the better known commercial varieties. The average waste in peeling 
all the potatoes handled during 1915, 1916, and 1917, a total weight 
of 233,492 grams, averaged 12.47 per cent, and the quantity of chips 
obtained averaged 29.85 per cent of the weight before peeling. In 
1915 the average loss for all lots was 13.16 per cent and the average 
weight of the chips produced was 27.43 per cent of the original 
weight of potatoes. In 1916 the loss through peeling alone averaged 
14.33 per cent ; through both peeling and slicing, 17.48 per cent ; and 
the quantity of chips produced averaged 30.22 per cent of the original 
weight. In 1917 the loss through peeling alone averaged 11.67 per 
cent; through peeling and slicing, 16.36 per cent; and the chips 
weighed 30.18 per cent of the original weight of potatoes. The 3- 
year average was therefore reduced by the 1915 figures, both the 1916 
and the 1917 averages being slightly over 30 per cent. Commercial 
men figure on getting between 15 and 27 per cent of chips from each 
barrel or sack of potatoes. Their percentages of waste in peeling 
are higher than the 12.47 per cent given here, for more careful meth- 
ods were employed in the laboratory than would be possible in a 
large factory. Langworthy 5 estimates the average waste in peeling 
potatoes to be 20 per cent, and with careless methods it may go even 
higher. 

The lowest possible percentage of waste in peeling may depend upon 
a number of factors, such as variety, place where grown, and condi- 
tion of the tubers (i. e., firmness, freedom from injury, decay, sprouts, 
etc.). The shape of the variety is one of the chief determining 
factors, for when the tuber is irregular, knobby, with deep or numer- 
ous eyes, it is practically impossible to prevent paring deeply. The 
skin itself varies slightly, being thicker on certain varieties, especially 
those with rough or netted exteriors. The influence of different soil 
types and environmental conditions sometimes causes a greater vari- 

6 Langworthy, C. F. Potatoes, sweet potatoes, and other starchy roots as food. U. S. 
Dept. Agr. Bui. 468, 29 p., 7 fig. 1917. 



METHODS OF MANUFACTURING POTATO (HIPS. 



17 



ation in shape, general appearance, and quality between specimens 
of the same variety grown in different parts of the country than is 
found in different varieties produced in the same locality. The con- 
dition of the tubers at the time of peeling also influences the per- 
centage of waste. The value of careful handling, though less popu- 
larly appreciated in the case of potatoes than with most perishable 
crops, has been clearly demonstrated. Cuts and bruises caused by 
careless methods of harvesting and handling are followed by decay 
in storage and make necessary much deeper paring into the flesh. 
Old potatoes that have softened and begun to sprout are much more 
difficult to peel economically. When the flesh is hard and firm the 
knife can shave off a thinner portion of crisp flesh than after some 
of the water has evaporated and some of the starch has been con- 
verted into sugar, leaving the flesh with a rubbery texture. 

Table 2. — Comparison of certain standard varieties of potatoes, shoiving the 
loss in peeling and slicing and the quantity of chips produced, Arlington 
Experimental Farm, 1915, 1916, and 1911. 



Varieties compared. 


Year. 


Weight 
unpeeled 
(grams). 


Averagt 
weight (i 


i loss in 
>er cent). 


Weight of chips per kilogram 
of potatoes (grams). 


By 

peeling. 


By peel- 
ing and 
shcing 


Un- 
peeled. 


Peeled. 


Sliced 
raw. 




f 1915 
{ 1916 
I 1917 


1,000 
4,417 
6, 377 


12.2 
16.8 
12.70 




272 

289.1 

305 


309.8 
347.5 
362.2 




Green Mountain 


21.46 
17.09 


368.2 




376.5 


2-year avearge, 1916 and 1917. 


10, 794 
11,794 


14.37 
14.10 


18.88 


307.1 
304.1 


358.6 
354.4 


378.6 


3-year average, 1915, 1916 
and 1917 








f 1915 
{ 1916 
{ 1917 








2,002 

2,192 

396 


13.49 
19.84 
19.95 




268.2 
264.6 
275.2 


305.4 
330.1 
343.8 




Irish Cobbler 


21.99 
22.72 


339.2 




356.2 


2-year average, 1916 and 1917. 


2, 588 
4,590 


19.86 
17.08 


22.10 


266.2 
265.3 


332.2 
320.0 


341.2 


3-year average, 1915, 1916, 
and 1917 








/ 1915 
\ 1916 








2,000 
2,581 


14.35 
9.26 




218.0 
275.1 


254.2 
303.1 




Rural New Yorker 


12. 55 






314. 5 


2-year average, 1915 and 1916 . 


4,581 


11.43 




250.1 


282.4 






f 1915 
\ 1916 
[ 1917 








1,000 

2,323 

285 


11.8 
10.8 
12.98 




321 
299. 2 
291.2 


363.9 
335.4 
334.7 




Early Ohio 


13.43 
17.19 


345.6 




351.7 


2-year average, 1916 and 1917. 


2,608 
3>608 


11.04 
11.25 


13.84 


298.3 
304.6 


335.3 
343.2 


346.2 


3-vear average, 1915, 1916 
and 1917..., 








| 1915 
\ 1916 
I 1917 








1,005 

2,008 

395 


9.25 

5.8 

6.83 




306.5 
325. 7 
308.9 


337.7 
345.9 
331.5 




Up-to-Date 


8.87 
11.39 


357.4 




347.6 


2-year average, 1916 and 1917. 


2,403 
3,408 


5.99 
6,95 


9.23 


304.1 
318.0 


321.3 
34a 9 


355.8 


3-year average, 1915, 1916 
and 1917 








/ 1916 
\ 1917 






Peachblow 


2,667 
374 


8.73 
7.22 


11.18 
11.50 


329.6 
334.2 


361.1 
360.2 


371.08 




37/. 6 


2-year average, 1916 and 1917 


3,041 


8.54 


11.21 


330.1 

I 


361. 


371.8 



18 



BULLETIN 1055, U. S. DEPARTMENT OF AGRICULTURE. 



Table 2. — Comparison of certain standard varieties of potatoes, showing the 
loss in peeling and slicing and the quantity of chips produced, Arlington 
Experimental Farm, 1915, 1916, and 1917 — Continued. 





Year. 


Weight 
impeeled 

(grams). 


Average loss in 
weight (per cent). 


Weight of chips per kilogram 
of potatoes (grams). 


Varieties compared. 


By 

peeling. 


By peel- 
in? and 
slicing. 


Un- 
peeled. 


Peeled . 


Sliced 
raw. 


Netted Gem (Colo.) 


1916 
1917 


1,586 
264 


9.98 
12.5 


12.42 
16.66 


319.0 
306.8 


354. 36 
350.6 


365.4 


Netted Gem (Me.) 


368.2 






2-year average, 1916 and 1917. 


1,850 


10.32 


13. 02 


317.2 


353.8 


364.8 




/ 1915 
I 1917 




fictmot Chili 


1,000 
492 


14.8 
13.6 




277 
315 


325. 1 
364.7 






17.2 


380.8 


2-year average, 1915 and 1917. 


1,492 


14.41 




289.6 


338.2 






f 1915 








1,000 
373 


12*5 
16.08 




234.0 
262.7 


267.4 
313.1 




Pearl \1917 


22.0 


336.8 


2-year average, 1915 and 1917. 




1,373 


13.47 




241.8 


279.4 










Bliss Triumph : i J 9 ,}^ 


1,000 
370 


14.0 
14.32 




197.0 
297.3 


229.1 
347.0 




18.9 


366.7 


2-year average, 1915 and 1917. 




1,370 


14.08 




224.0 


260.8 










Early Manistee { Jj^ 


994 
321 


18.41 
7.16 


20.32 
9.97 


308.9 
314.6 


378.6 
338.9 


387.6 
349.5 


2-year average, 1916 and 1917. 




1,315 


15.66 


17.79 


310.2 


367.9 


377.4 






Eldorado : { J 9 ^ 


1, 000 
210 


14.2 
10. 00 


17.5 
16.19 


319.0 
304.7 


371. 8 
338.6 


386.7 
363.6 


2-year average, 1916 and 1917. 




1,210 


13.47 


19.96 


316.5 


365.8 


382.6 






Rural Blush 


f 1916 
\ 1917 

/ 1916 
\ 1917 


432 
297 


33.8 
12.45 


36.34 
16.83 


240.7 
285.0 


363.7 
353.8 


378.2 




372.4 


2-year average, 1916 and 1917. 


729 


25.10 


28.39 


268.8 


358.8 


375.3 


Mclntyre 


387 
298 


16.79 
16.10 


18.34 
21.81 


320.5 
268.4 


385.1 
320.0 


392.4 




343.3 


2-year average, 1916 and 1917. 


685 


16.49 


19.85 


297.8 


356.6 


378.8 




/ 1916 
\ 1917 




Hamburger Eier 


196 
252 


16.83 
13.89 


20.41 
22.62 


295.9 
277.8 


355.8 
322.5 


371.8 




359.0 


2-year average, 1916 and 1917. 


448 


15.17 


21.65 


285.7 


336.8 


364.3 




( 1915 
\ 1916 
I 1917 




1-year average of all seed- 
lings and varieties 

2-year average, 1916andl917. 


24, 695 
130, 764 

78, 033 
208, 797 

233, 492 


13.16 
14.33 
11.67 
12.39 

12.47 




274.3 
502. 2 
301.7 
301.9 

298.5 


310.8 
349.2 
341.9 
343.4 

341.0 




17.48 
16.36 
16.56 


363.1 
361.6 
361.2 


3-year average, 1915, 1916, 
and 1917 















When the potatoes are sound and in good condition most of the 
12.47 per cent waste in peeling is composed of flesh around the eyes. 
If the eyes are deep it is not possible to gouge them out with a knife 
as carefully as the skin is removed by the peeler. This loss is less 
important than an equally deep peeling elsewhere, however, for the 
internal medulla extends a branch to each eye, lessening the propor- 
tion of dry matter to water and reducing accordingly the food value 
of the flesh. East 6 has shown that the quality of the potato varies 

"East, Edward M. A study of the factors influencing the improvement of the potato. 
111. Agr. Exp. Sta. Bui. 127, p. 375-450, 10 fig. Bibliography, p. 450-456, 1908, 



METHODS OF MANUFACTURING POTATO CHIPS. 



19 



inversely with the number of eyes, and that there is great variation 
within the variety. 

Table 3 shows that approximately half a pound of oil was used 
for every pound of chips produced, or, to be more exact, 0.451 pound 
in 1916 and 0.434 pound in 1917. This was slightly less than the 
estimates furnished by two manufacturers of potato chips. Not all 
of this oil went into the chips, however, a great deal being lost 
through spattering over the pan, in draining the chips, and in strain- 
ing the oil. 

Table 3. — Ratio of cottonseed oil required for making potato chips, tests* of 

1916 and 1917. 





Number 
of tests. 


Average weight 
(grams). 


Ratio. 




Oil used. 


Chips 
made. 


Oil. 


Chips. 


1916 

1917 


47 
33 


369 

312.45 


818 
718. 66 


0.451 
.434 


1 
1 



SUMMARY. 

Potatoes are a universal article of diet, and their home manufacture 
into potato chips is entirely feasible. High-grade cottonseed oil 
heated to approximately 210° C. (400° F.) is the best fat in which to 
fry them. Vegetable oils or compounds are more satisfactory than 
animal fats, and liquids are somewhat preferable to the semiplastic 
compounds. No fat with a smoking point of less than 220° C. 
(428° F.) is satisfactory. The oil should be entirely renewed every 
second or third day when chips are manufactured in commercial 
quantities. 

Mechanical peelers are necessary for commercial production and of 
great assistance in home manufacture. Vegetable slicers are essential 
for uniform results, as it is impossible to cut potatoes thinly and 
evenly enough by hand. 

The best vessel in which to fry the chips is one that is deep rather 
than wide, made of iron or steel, with an inner perforated basket in 
which the chips can be lowered and raised. 

Use mature potatoes, high in starch. Large or medium-sized, round 
potatoes with shallow eyes are preferable. The slices should be thor- 
oughly washed in cold water and a maximum of starch removed. 

In the experimental tests of the Bureau of Plant Industry, potato 
chips were scored on a basis of 30 points, distributed as fellows : Ease 
of cooking, 10 ; appearance, 5 ; crispness, 5 ; flavor, 10. 



20 



BULLETIN 1055, U. S. DEPARTMENT OF AGRICULTURE. 



The average waste in peeling all potatoes handled during 1915, 
1916, and 1917 was 12.47 per cent, and the quantity of chips produced 
averaged 29.85 per cent of the weight before peeling. Commercial 
men figure on getting between 15 and 27 per cent of chips from each 
barrel or sack of potatoes. 

Approximately half a pound of oil was used for every pound of 
chips produced. 

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